A bulky filter tow is packed in a state of compressed filter tow bale.
As packed tow bales are stored in a warehouse in a multistage stacked manner, a technology for facilitating the multistage stacking is provided.
In JP-A 2005-528096, there is disclosed a technology in which a tow bale is packaged with a plastic film and the inside of the tow bale is made to be in a negative pressure state, thereby allowing a top surface and a bottom surface of the tow bale to be flat surfaces.
In JP-A 2009-508764, there is disclosed an invention in which a fiber material is packaged after being compressed by use of a convex bale platen to manufacture a fiber bale.
As shown in FIG. 2 and FIG. 3, the convex bale platen 18 has a shape in which the entire convex surface 20 is curved.
When the fiber material is compressed by using the convex bale platen 18 having the above shape, a central part of the fiber material is strongly compressed, and the compression in a peripheral part is low. Therefore, after releasing the compression, the degree of swelling in the central part is small and the swelling in the peripheral part is large. As a result, the entire surface becomes flat.
In JP-A 2008-539143, there is disclosed a method of compressing a fiber material by using a platen.